Interlayers have been used in multicolor photographic elements to aid in differential processing of various silver halide emulsions after exposure and to minimize the effects of one layer of the element on another when both are simultaneously undergoing treatment as disclosed by Neblett, Photography, Its Materials and Processes, 1962, Chapter 33. The use of improved interlayers in a multicolor image transfer film unit is well known, as disclosed in, for example, U.S. Pat. Nos. 3,411,904 and 3,418,117, both by Becker. The interlayers in many of the known film units act as temporary barriers to isolate the reactants of the surrounded layers for a predetermined length of time.
Image transfer processes that employ a single processing solution to develop an exposed image record and produce a viewable image record are well known in the art. In many instances, after-treatments such as washing or stabilizing baths are not used in these image transfer processes, since the element is a fully self-contained film unit.
In certain instances, various barrier layers, timing layers, or spacer layers have been used in image transfer film units to delay action between the ingredients of various layers of the film unit. Barrier layers have been used between polymeric acid layers and the silver halide emulsion layers of an image transfer film unit to allow processing to continue at a high pH for a predetermined period of time before the acid layer becomes effective in neutralizing the processing composition as disclosed in U.S. Pat. No. 2,584,030, issued Jan. 29, 1952.
The use of barriers or spacer layers employed in conjunction with neutralizing layers in one commercial image transfer product is described by Friedman, History of Color Photography, 1968, pages 538-543. In products of this type, the alkaline composition penetrates through the barrier layer and alkali is depleted throughout the structure by the acid in the neutralizing layers. In certain instances, breakdown of the barrier layers releases the materials that serve as a shutoff mechanism, establishing the amount of silver halide development and the related amount of dye formed according to the respective exposure values.
Many of the photographic development processes utilized in image transfer film units is temperature dependent. At relatively low temperatures, the development process is slower while at relatively higher temperatures, the development process is faster. This temperature dependence of development ratecan cause adverse effects on the quality of the image formed in an image transfer film unit. At colder temperatures, the breakdown of the barrier layer (which leads to shutdown of the development reaction) may occur before the slower development process is completed. At warmer temperatures, the development process may proceed too far before the barrier layer breaks down. It is therefore desirable to have a barrier layer that becomes more alkali-permeable at higher temperatures and less permeable at lower temperatures in order to compensate for the temperature dependence of the development reaction rate.
The temperature dependence of the alkali-permeability of a polymer can be measured by its activation energy, and should correspond with the temperature dependence of the particular development chemistry so that neither overdevelopment nor underdevelopment occurs across the range of temperature conditions under which the image transfer film unit will likely be used. Activation energy in Kcal/mole is determined from the slope of the straight line potion of the curve according to the formula: ##EQU1## A discussion of activation energy calculations can be found in Kinetics and Mechanism 2d, John Wiley & Sons, New York, 1961, pp. 22-25.
Many layers contained in image transfer film elements utilize gelatin as a binder or vehicle. It is advantageous if temporary barrier layers used in such elements are compatible with gelatin, i.e., they can be coated from aqueous solutions. Microgel polymers are highly compatible with gelatin and gelatin coating systems. U.S. Pat. No. 4,504,569 discloses chill-gelable microgel temporary barrier layers comprising cross-linked N-alkyl-substituted acrylamide polymers. These polymers, however, have a negative activation energy, rendering them unsuitable for many applications.
It would therefore be desirable to have a polymer for use as a temporary barrier layer that has a positive activation energy that is compatible with photographic development chemistry used in image transfer film units and that is a microgel compatible with aqueous gelatin systems.